Mata was not a contender for the man of the match award against Basel on Tuesday night but his influence was noticed by the United supporters who applauded him off heroically in the second-half.

Mourinho has hailed Mata's brain (Image: REUTERS)

They noticed the difference from the team which attacked turgidly without Mata at Stoke and he might be the difference in United's quest for a 21st title.

His omission in the Potteries sparked a formation change which hampered Henrikh Mkhitaryan and deprived United of an additional attacker.

With Mata back in against Basel, United reverted to 4-2-3-1 and played expansive and creative football which their visitors could not weather.

The irony in Mata's increasing importance extends beyond Mourinho's reliance on a playmaker he discarded.

The Spanish star is now a favourite for Mourinho (Image: Manchester United)

Louis van Gaal gave the impression Mata could only function on the right wing in a 4-3-3 with Ander Herrera as his foil.

The Dutchman's inexplicable switch to 4-2-3-1 in summer 2015 claimed various victims but Mata was so ostracised from his teammates he might as well have sat in row A.

United players were so rigidly fixed to their formations they resembled schoolchildren playing stuck in the mud in a playground.

When Mata is surrounded with pace and movement it is immaterial whether he plays on the right or at 10, or what the formation is.

He is flourishing with more freedom (Image: Manchester United)

Van Gaal discovered that with a couple of wins over Derby and Stoke early last year.

"Sparkling football," was his verdict, as Mata lined up behind Wayne Rooney with Jesse Lingard to his right.

Lingard scored against Stoke and netted another five days later by interchanging with Mata. He is not the only forward buoyed by the Spaniard.

Mourinho could be seen instructing Mata and Rashford to switch during the FA Cup victory over Reading in January, which might be the only game Rashford thrived in while playing on the right wing.

Mata found himself cast aside at Chelsea under Mourinho (Image: Laurence Griffiths)

Mkhitaryan's understanding with Mata is rooted in selflessness; two playmakers who do not compete with each other.

Beyond his commendable Common Goal initiative, blog posts and abrazos he offers supporters, Mata is a steely soul and there was a flash of that streak during that brief and tetchy exchange with Mourinho during the Community Shield before the United manager defused the situation.

Mourinho identified Mata as a weakness upon his appointment and reinforced United on the right flank with Mkhitaryan yet Mata continued to rail against the doubters. Dropped last September, he returned to the side in a 4-3-3 - playing as the right central attacking midfielder - and scored superbly as United blitzed Leicester.

Mata's mind is as vital to United as his skills (Image: Getty Images Europe)

United have played their most zestful football under Mourinho with Mata in the side and he has made a mockery of the inflexible Van Gaal by flourishing in different formations and different positions he was not previously considered for.

It might be disingenuous to dub Mata and Mourinho's matrimony as a marriage of convenience. Mata was nervous about the prospect of Mourinho replacing Van Gaal and according to a source hoped Luis Enrique - a man who was never in the reckoning - would replace the Dutchman.

As soon as it became apparent Mourinho would replace Van Gaal Mata's mood was one of insouciance and he let it be known he had no issues with Mourinho over his Chelsea departure.